Apple loves water sensors, which it calls 'liquid contact indicators': in the new Retina MacBook Pro, there are no less than 10 of them.
Red stars show sensors that are hidden under a cable or another component and the blue dots show sensors directly visible when the bottom plate is removed.
Until now, only a few models of 17" MacBook Pro and MacBook Air had 8 of those sensors, the control level is now going up with 10.
Apple keeps saying that these sensors are only there to indicate wether they were in direct contact with liquid and that there is no reason for them to turn red in normal conditions of use, within the limits of temperature and humidity.
As a reminder, these sensors are among the first things that are checked by Apple technicians when fixing a device under warranty, therefore be careful with liquids getting too close to your computer. Since this new model is so integrated, everything is tightly fitted inside the aluminum casing and liquid will spread easily through many components. The cost of repair could go up pretty fast!